Air-water-fertilizer-coupling Drip Irrigation Facilitates Lettuce Growth by Shaping Rhizosphere Microbiome Associated with Soil Nutrient Cycling

Air-water-fertilizer-coupling drip irrigation is an emerging technique to promote crop growth by improving soil properties. How the rhizosphere microbiome responds to air-water-fertilizer coupling and relates to soil fertility and crop growth is still poorly understood. The aim of this study was to explore the effects of various drip irrigation regimes on the growth of greenhouse lettuce, soil fertility, and rhizosphere microbiome structure. A pot experiment was conducted under different levels of air void fraction (5 and 20 mg L^− 1 of dissolved oxygen), irrigation volume (90% and 60% of field capacity), and organic fertilizer amount (50, 37.5, and 25 g kg^− 1 of chicken manure). Air-water-fertilizer coupling lowered pH values and increased organic matter, nitrate nitrogen, available phosphorus, and available potassium contents in the rhizosphere soil. The diversity and richness of rhizosphere bacterial communities were highest in soil samples under the high fertilizer and high water levels with aeration. Root-zone aeration (20 mg L^− 1 of dissolved oxygen) contributed to the abundance of Actinobacteria that could promote plant growth (13.3% increase) compared with the non-aeration treatment (5 mg L^− 1 of dissolved oxygen). The opposite effect of aeration was observed for Gammaproteobacteria comprising harmful pathogens (7.13% decrease). Increasing the level of organic fertilizer amount resulted in the enrichment of Proteobacteria and depletion of Acidobacteria, despite no significant difference in the relative abundance of Proteobacteria between the high and medium fertilizer levels. Lettuce plants showed enhanced biomass accumulation and improved root morphology and activity under air-water-fertilizer coupling, but the aboveground biomass and root morphology did not differ significantly between the high and medium fertilizer levels. High levels of air void fraction (20 mg L^− 1 of dissolved oxygen) and irrigation volume (90% of field capacity) with a medium level of organic fertilizer (37.5 g kg^− 1) are recommended for greenhouse lettuce in terms of economic benefits and crop productivity.